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Homo heidelbergensis

Introduction

In 1907, at the Mauer sand pits in Germany, a nearly complete mandible was discovered by a quarry
worker. This mandible (Mauer 1) validated Otto Schoetensack's conviction that there would be Pleistocene human
remains found in the quarry amid the more common rhino, bear, elephant, bison, deer, and horse remains.
Schoetensack published an extensive monograph on the mandible a year later in which he designated it
to a new species of hominid, Homo heidelbergensis. Schoetensack named a new species without
justifying it by describing the unique anatomical features of the species. Along with this lack of
morphological comparisons and differentiation from other known species, the lack of older specimens
(and just about any specimen at all for a long period of time) kept heidelbergensis from
becoming accepted among paleoanthropologists.

However, though Schoetensack did not justify his species designation, there are features that set
Mauer 1 apart from Neanderthal and H. sapiens. The age of the specimen also creates a distinction,
as it dates to appromiately 500 kyr. With a wealth of newer discoveries in the last 30 years, the species
designation if heidelbergensis has been revived. The validity of heidlebergensis seems
to be current among many researchers at this time, but it is by no means universally accepted. Many researchers
argue that heidelbergensis is invalid, and is simply a chronospecies (though, that is exactly
what some proponents argue for, among those who see anagenesis as a valid speciation event).

In this overview of the species, I will be making the distinction of heidelbergensis from
erectus based on both age and geographic location. Starting with the null hypothesis that
all the ergaster, erectus, and heidelbergensis are members of the same variable
species that differ by age and geography, I will discuss heidelbergensis as those specimens
occurring later, and occurring in Europe and Africa. I will discuss erectus as those specimens
occurring earlier and in Asia and Africa. My personal convictions are not contained in this partition
of the specimens, as I am trying to give a current overview of popular opinion in the field while noting
obvious fallacies in some species designation (as per antecessor).

Diagnostic Features

Due to the fact that there have been so many different specimens attributed to the erectus
offshoots, it is difficult to create a list of features that differentiate heidelbergensis
from erectus or H. neanderthalensis. In general, heidelbergensis specimens show
a continuation of evolutionary trends that occurred in the Lower Pleistocene into the Middle Pleistocene.
Along with changes in robustcity of cranial and dental features, there is a marked increase in brain size
from erectus to heidelbergensis. Some of the features of Middle Pleistocene Homo
that shows these trends include:

A shift from the widest part of the brain case from the cranial base to the parietal regions.

The rear of the cranial vault becomes more vertical.

A gradual reduction in cranial robusticity.

A decline in postcranial robusticity also.

A tendency for a shift from shorter more robust stature to taller more leaner bodies.

The increase in brain size may have also come with an increase in brain complexity, although this
is difficult to determine from endocasts, and may have to remain supposition only. However, the increase in
absolute size, and the change to larger frontal and parietal lobes indicate that there may have been a
reorganization of the functional anatomy of the hominid brain. The increase in size itself indicates
changes in behavior that lead to the ability to more easily acquire nutritional resources. This is due
to the high nutrition requirements of brain tissue, especially during development. There is increasingly
more convincing evidence in the use and control of fire, and in the hunting of animals for food. This
time period is important for many reasons, and may be the time period when more modern behavior began to
develop.

The type specimen of heidelbergensis is Mauer 1. This specimen shows a host of both primitive
and derived features that, in general, have been accepted as proof of ancestry to the Neanderthal line. The
specimen was discovered in 1907 in the Mauer sand pits near Heidelberg, Germany. The exact age of the
specimen is uncertain, but it dates at least as old as 400 kyr, and possibly as old as 700 kyr. However,
a date of 500 kyr is generally accepted as most likely. Some of the traits that distinguish this specimen
include:

A sloping symphysis that contains two mandibular tori on its inner side (primitive).

An especially broad ramus (primitive).

An M2 that is larger than the M1 (primitive).

A very robust mandible (primitive).

Taurodont molars (derived).

A reduced M3 (derived).

Dramatic buccal cusp dominance in the P3 (derived).

Another Middle Pleistocene hominid that may or may nor be attributed to heidelbergensis is
the Bodo cranium. Bodo was discovered in 1976 at Bodo d'Ar, Ethiopia, in the Middle Awash Valley.
The specimen is important because of its age (600 kyr), and its suit of features. The cranium
is extremely robust and sports the biggest face known among hominid specimens. Acheulean tools
were found near the site with the remains of hippos, baboons, and antelopes, indicating that
Bodo may have been butchering animals for meat, and may have even hunted them. However, Bodo
himself was also the victim of butchery, as seen by the distinctive cutmarks on several parts of
the cranium. Bodo has also been at the center of infighting among scientists, and, as such, has had
relatively few publications describing it. Some of the features that distiguish Bodo include:

Approximately 1100cc brain.

A broad massive face.

An extremely broad nose (the largest of any Pleistocene hominid).

The lower nasal margin is guttered.

Robust zygomatics that angle backwards from the nasal margins.

An expanded maxilla, and an associated lack of a canine fossa (though there is a very shallow
fossa lateral to the nose).

A long sloping frontal bone.

A thick browridge with a fery deep temporal fossa.

A remarkably flexed cranial base.

A flat sloping anterior face on the mandibular fossa, that is the result of emphasis on anterior
tooth loading.

The cave site of Arago, at Tautavel, France, in the eastern Pyrenees mountains has yielded the remains
of many hominids, with the cranium Arago XXI the most complete. Due to its size and robust facial
features, Arago XXI is generally considered a young male, though some consider it female. The dating of the material is problematic, with
a wide range of dates being claimed. Henry de Lumley considers the material to be approximately 400 kyr, though
it is much more likely that the material dates 200 kyr to 300 kyr. Arago 21 is fairly complete,
lacking only the temporal and occipital bones. Some of its distinguishing features include:

An approximately 1166cc brain.

Broca's cap and other speech areas are well-developed.

Evidence of an extensive right parietal association area.

Evidence of right-handedness from an asymmetric endocast.

Lacks a frontal boss.

Presence of marked parietal boss.

Presence of an angular torus.

A low broad sagittal keel.

A deep supraorbital sulcus.

A short and prognathic face, with an expanded maxilla.

The material from Petralona is very similar morphologically to the Arago material. The Petralona 1
cranium was discovered in 1960, hanging suspended from a stalagmite in a cave of Katsika Hill, in
Petralona, Greece. The specimen has a very ambiguous morphology, which led to several different species
attributions. It was originally attributed to neanderthalensis, and was later classified as
erectus, but it falls much closer to the morphology of the various heidelbergensis specimens,
especially Arago XXI. The specimen was originally thought to be approximately 70 kyr, as young as
many Neanderthal specimens, and later estimates put that number at closer 700 kyr. However, ESR dating has
given a date of between 247 kyr and 127 kyr, though some researchers estimate its likely date to be around
300-400 kyr due to its morphology. Some of its features include:

A large brow ridge - a double-arched supraorbital torus.

Lacks a canine fossa.

An open occipital angle.

A 1220 cc brain estimate.

A massive face, though it is non-projecting.

A prominent transverse torus.

There are many other specimens that can be (and have been) attributed to heidelbergensis, and
they generally have all the same common traits that have been mentioned for the specific specimens
discussed above. Material from Apidima, Kabwe, Steinheim,
Atapuerca, etc. can be and have
been designated as heidelbergensis, or erectus. In general, there is a decrease in
robusticity, an increase in brain size, and a tendency towards more derived features of neanderthalensis
or sapiens.

Conclusions

There is no real question as to whether or not heidelbergensis is a chronospecies, it is. The
validity of it depends on whether one accepts anagenesis as a valid method of speciation. H. heidelbergensis
specimens are generally Middle Pleistocene hominids in Europe or Africa (though some specimens from
Asia such as Dali have been designated to heidelbergensis by a few individuals), with the major
difference from erectus being spatial.

Bibliography

This bibliography contains the sources of the information cited above, as well as any sources that
could provide any other information on the subject. If you know of any other sources that are pertinent
to H. heidelbergensis, please e-mail me the citation in the format used below, and I will add it
to the list. Any problems with information I presented above can be sent to me
here. I don't want to provide misinformation, and any corrections are gladly accepted (with
proper documentation of what is wrong and why, with sources). Thanks!

Adam, K.D. 1985. "The chronological and systematic position of the Steinheim skull." In
Ancestors:
The Hard Evidence, ed. by E. Delson, pp. 272-276. New York: Alan R. Liss.